Considerable effort has been directed to the improvement of induction machine circuits, particularly since the development of the solid state switches capable of handling large power levels. Solid state inverters have been developed for use in connection with such machines to provide an alternating output voltage from a d-c input voltage. In studying such arrangements, it was found that after the machine was initially energized, the energization could be removed and the machine's operation maintained as energy is recirculated from the machine through the inverter switches and back to another phase winding of the machine. This discovery was described and claimed in U.S. Pat. No. 3,829,758.
In subsequent work the basic circuitry of the machine-inverter combination has been carefully analyzed, and it now appears that one means of sustaining the field energy of the generator is by periodically short circuiting the terminals of the inverter. This analysis represents a significant contribution of the present invention because, based on this analysis, it is possible to derive and implement a substantially simplified switching arrangement for regulation of the induction machine.
It is therefore a principal object of this invention to provide a system for sustaining the electrical field of an induction generator by periodically shorting the generator terminals.
A closely related object of the invention is to provide a switch arrangement for shorting the generator terminals, with an accompanying control circuit, which is considerably simplified and less expensive than prior art systems.